FIG. 1 shows a conventional liquid infusion apparatus having a driving means comprising a CPU 1, a motor driving circuit 2, a potentiometer output processing circuit 3, an encoder output processing circuit 4, a motor 5, gears 6, a feed screw 7, a carriage 8, a slider 9 (plunger pushing out portion), a rotary encoder 10, a potentiometer 13, a hook 11 for operating the potentiometer 13, a wire 12, a syringe 14, and a plunger 15. In said conventional infusion apparatus shown in FIG. 1, the syringe 14 having the plunger 15 therein is mounted stationarily. The feed screw 7 is arranged in parallel with said syringe 14, connected to the motor 5 through the gears 6, and brought into engagement with the carriage 8. The slider 9 is connected to the carriage 8 and brought into engagement with an end of the plunger 15. The rotary encoder 10 is connected to the motor 5 or the feed screw 7. The potentiometer 13 is arranged at a position in parallel with the feed screw 7. The hook 11 is connected to an end of the wire 12 for rotating said potentiometer 13 and arranged so as to engage with the carriage 8 when the carriage 8 is moved to a remaining liquid quantity small section. The output of the rotary encoder 10 is applied to the CPU 1 through the encoder output processing circuit 4 and processed. The output of the potentiometer 13 is applied to the CPU 1 through the potentiometer output processing circuit 3 and processed. The motor is driven by a signal from the CPU 1 through the motor driving circuit 2, so that the plunger 15 is pushed out at a predetermined speed through a predetermined length to exhaust the liquid in syringe 14.
A further or second conventional liquid infusion apparatus shown in the Japanese Patent Application Laid-Open No. 42218/93 comprises a driving means for driving a plunger of a syringe to move at a predetermined speed between a first and a second positions, and a first linear encoder arranged between a third and fourth positions corresponding to the first and second positions, respectively, for detecting the absolute position and the moving distance of said plunger. FIG. 2 shows the essential portion thereof.
In the first conventional apparatus, no actual feeding quantity of the carriage can be detected in case that a slip is generated about the feed screw or the motor, or the carriage is floated on the feed screw, and no actual position of the remaining liquid quantity small section can be detected in case that the wire is cut, or the contact of the electric terminal of the potentiometer is failure. Further, in the second conventional apparatus, such problems that the actual feeding quantity of the carriage can not be detected because of the slip about the feed screw or the motor, or of the floatation of the carriage on the feed screw can be solved, because in the second conventional apparatus, the moving state of the carriage is detected by the linear encoder. However, the second conventional apparatus has such a problem that the linear encoder for detecting the absolute value is expensive and the skill is required. Accordingly, an object of the present invention is to provide a liquid infusion apparatus having a driving means which can detect exactly and control the movement of the plunger so as to solve the above problems.
Further, Japanese Patent Application Laid-Open No. 44390/88 discloses an improved liquid infusion apparatus comprising a feed screw to be driven by a prime mover, and a slider movable linearly, wherein the slider is brought into engagement with said feed screw so as to push out a plunger in a syringe and to exhaust liquid in the syringe, and a pressure exerted on the plunger by the slider is detected and compared with a reference value to generate a warning signal.
In said liquid infusion apparatus, a pressure sensor is provided at a plunger pushing portion of the slider and an output of the sensor is compared with a plurality of reference values so as to generate the warning signal and to carry out safely the infusion. As shown in FIG. 3, however, in said liquid infusion apparatus an end of the plunger is brought into contact simply with the slider, and accordingly in case that the plunger is sucked into the syringe by an attractive force due to the negative pressure applied to the syringe, the slider is brought into disengagement with the plunger, so that the liquid infusion cannot be attained, but such state cannot be detected. Accordingly, the other object of the present invention is to provide a liquid infusion apparatus which can detect the negative pressure applied to the plunger.
FIGS. 4A and 4B are views explaining the operation of the other conventional liquid infusion apparatus. FIG. 4A shows such a state that the syringe 14 and the plunger 15 are not yet mounted on the main body of the apparatus. FIG. 4B shows such a state that the syringe 14 and the plunger 15 are mounted on the main body. In FIGS. 4A and 4B, a reference numeral 14-1 denotes a flange of the syringe 14, a reference numeral 15-1 denotes a flange of the plunger 15. A reference numeral 16 denotes a slider, 16-1 denotes a holding member provided at the slider 16 for holding the flange 15-1 of the plunger 15, 16-2 denotes a pushing portion of the slider 16, 16-3 denotes a grooved portion formed on the holding member 16-1, and 17 denotes a lever of a slider unlock means (not shown). A reference numeral 17-1 denotes a push button of the lever 17, 17-2 denotes a pivot shaft of the lever 17, 21 denotes a main body of the liquid infusion apparatus, and 21-1 denotes a groove provided at the main body 21 for receiving therein the flange 14-1 of the syringe 14. In order to install the syringe 14 and the plunger 15 to the main body 21 of the liquid infusion apparatus shown in FIG. 4A, the slider 16 is disengaged from the feed screw 7 by pushing the pushing button 17-1 of the lever 17, the slider 16 is moved toward the flange 15-1 of the plunger 15, and the pushing portion 16-2 is brought into contact with an outer end of the plunger 15, so that the syringe 14 and the plunger 15 are fixed to the main body 21 as shown in FIG. 4B. The width of the grooved portion 16-3 is determined corresponding to the maximum thickness of the flange 15-1 of the plunger 15.
In the above conventional apparatus, however, the width of the grooved portion 16-3 of the holding member 16-1 is fixed, and accordingly, if the thickness of the flange 15-1 of the plunger 15 is smaller than that of the grooved portion, the plunger 15 cannot be held positively by the slider 16.
Further, in a liquid infusion apparatus wherein the liquid infusion is carried out automatically by moving the plunger of the syringe using a motor, it is necessary absolutely to prevent the plunger from moving in a (suction) direction contrary to the pushing direction of the plunger. Accordingly, in the conventional liquid infusion apparatus, the rotary direction of the motor is limited to only one direction by a motor driving program and an electric circuit thereof.
Recently, however, most of electric appliances generate many kinds of electric noises (electromagnetic waves) according to the development of the electronic systems, so that many problems of wrong operation due to the noises have been encountered in the field of the medical services.
Further, Japanese Utility Model Application Laid-Open No. 89053/83 discloses an improved liquid infusion apparatus comprising a feed screw driven by a prime mover, and a slider movable linearly, engaged with the feed screw so as to push out the plunger of the syringe and infuse liquid from the syringe, wherein the engagement and disengagement of the slider with the feed screw can be carried out corresponding to that of the slider with the syringe. In said conventional infusion apparatus, as shown in FIGS. 5A and 5B, a sliding means is provided at a driving pawl which is fitted into a driving member when the syringe is installed on the main body, so that a feed screw is disengaged from a half-nut fixed to said driving member at the same time of the sliding of the driving pawl. Japanese Patent Application Laid-Open No. 247347/91 discloses a further conventional liquid infusion apparatus as shown in FIG. 6. In this apparatus, a movable block is provided movably reciprocally in an axial direction of a syringe and connected to a driving means, and a pushing portion of a plunger is provided at the movable block movably reciprocally between a position where the pushing portion is engaged with the plunger and a position where the pushing portion is disengaged from the plunger, and a half-nut is engaged with and disengaged from a feed screw according to the movement of the movable block.
The apparatus shown in FIGS. 5A and 5B, or shown in FIG. 6 has such problems that in the loading state the half-nut is floated on the feed screw, because the half-nut is normally urged to the feed screw by a spring, so that the precise feeding operation cannot be carried out. Further, in the conventional apparatus, operations for engaging the plunger with the slider and for disengaging the plunger from the slider are carried out at the same time with operations for engaging the feed screw with the half-nut and for disengaging the feed screw from the half-nut. However, only a simple groove is provided at a holding portion of the slider for holding a flange of the plunger, so that the flange of the plunger is held unsteadily by the holding member due to the difference between the thickness of the flange of the plunger and the width of groove formed on the holding portion of the slider, which are generated by the mechanical precision. In the conventional apparatus mentioned above, it is preferable generally to shape the feed screw so as to have teeth of rectangular in cross section, which is in parallel with a vertical plane normal to the feeding direction of the feed screw, in order to prevent the half-nut from floating from the feed screw in case of loading. However, there are two problems. One problem is that the feed screw having teeth of the rectangular cross section is high in manufacturing cost, because the manufacturing steps thereof are limited. The other problem is that the flange of the plunger cannot be held precisely by the holding member, because a gap is formed between the flange of the plunger and the groove of the holding member due to the manufacturing precision.
The task of the present invention is to solve the above problems and to provide a liquid infusion apparatus of high precision and inexpensive.